Direct gene transfer into peanut intact embryonic leaflets was performed through electroporation. In transient beta -glucuronidase expression assays, maximal expression was obtained by using pulses of 625 V cm(-1) in EPRm (modified electroporation) buffer supplemented with 75 muM NaCl. Kanamycin-resistant plants were obtained, and the presence of the nptII gene was demonstrated by PCR analysis. The positive effect electroporation on the efficiency of in vitro regeneration was demonstrated. Explants submitted to field strengths between 500 and 625 V cm(-1) displayed a significantly increased number of shoots and originated faster growing calluses relative to control explants. Whereas in control explants callus formation occurred only at the petiolule, electroporated leaflets developed additional organogenic calluses on the foliar lamina.